MEDIUM: activity: collect memory allocator statistics with USE_MEMORY_PROFILING

When built with USE_MEMORY_PROFILING the main memory allocation functions
are diverted to collect statistics per caller. It is a bit tricky because
the only way to call the original ones is to find their pointer, which
requires dlsym(), and which is not available everywhere.

Thus all functions are designed to call their fallback function (the
original one), which is preset to an initialization function that is
supposed to call dlsym() to resolve the missing symbols, and vanish.
This saves expensive tests in the critical path.

A second problem is that dlsym() calls calloc() to initialize some
error messages. After plenty of tests with posix_memalign(), valloc()
and friends, it turns out that returning NULL still makes it happy.
Thus we currently use a visit counter (in_memprof) to detect if we're
reentering, in which case all allocation functions return NULL.

In order to convert a return address to an entry in the stats, we
perform a cheap hash consisting in multiplying the pointer by a
balanced number (as many zeros as ones) and keeping the middle bits.
The hash is already pretty good like this, achieving to store up to
638 entries in a 2048-entry table without collision. But in order to
further refine this and improve the fill ratio of the table, in case
of collision we move up to 16 adjacent entries to find a free place.
This remains quite cheap and manages to store all of these inside a
1024-entries hash table with even less risk of collision.

Also, free(NULL) does not produce any stats. By doing so we reduce
from 638 to 208 the average number of entries needed for a basic
config using SSL. free(NULL) not only provides no information as it's
a NOP, but keeping it is pure pollution as it happens all the time.

When DEBUG_MEM_STATS is enabled, malloc/calloc/realloc are redefined as
macros, preventing the code from compiling. Thus, when this option is
detected, the macros are undefined as they are pointless there anyway.

The functions are optimized to quickly jump to the fallback and as such
become almost invisible in terms of processing time, execpt an extra
"if" on a read_mostly variable and a jump. Considering that this only
happens for pool misses and library routines, this remains acceptable.

Performance tests in SSL (the most stressful test) shows less than 1%
performance loss when profiling is enabled on 2c4t.

The code was written in a way to ease backporting to modern versions
(2.2+) if needed, so it keeps the long names for integers and doesn't
use the _INC version of the atomic ops.

src/activity.c

@@ -20,6 +20,14 @@
 #include <haproxy/stream_interface.h>
 #include <haproxy/tools.h>
 
+#if defined(DEBUG_MEM_STATS)
+/* these ones are macros in bug.h when DEBUG_MEM_STATS is set, and will
+ * prevent the new ones from being redefined.
+ */
+#undef calloc
+#undef malloc
+#undef realloc
+#endif
 
 /* bit field of profiling options. Beware, may be modified at runtime! */
 unsigned int profiling __read_mostly = HA_PROF_TASKS_AOFF;
@@ -56,6 +64,261 @@ struct memprof_stats {
 /* last one is for hash collisions ("others") and has no caller address */
 struct memprof_stats memprof_stats[MEMPROF_HASH_BUCKETS + 1] = { };
 
+/* used to detect recursive calls */
+static THREAD_LOCAL int in_memprof = 0;
+
+/* perform a pointer hash by scrambling its bits and retrieving the most
+ * mixed ones (topmost ones in 32-bit, middle ones in 64-bit).
+ */
+static unsigned int memprof_hash_ptr(const void *p)
+{
+	unsigned long long x = (unsigned long)p;
+
+	x = 0xcbda9653U * x;
+	if (sizeof(long) == 4)
+		x >>= 32;
+	else
+		x >>= 33 - MEMPROF_HASH_BITS / 2;
+	return x & (MEMPROF_HASH_BUCKETS - 1);
+}
+
+/* These ones are used by glibc and will be called early. They are in charge of
+ * initializing the handlers with the original functions.
+ */
+static void *memprof_malloc_initial_handler(size_t size);
+static void *memprof_calloc_initial_handler(size_t nmemb, size_t size);
+static void *memprof_realloc_initial_handler(void *ptr, size_t size);
+static void  memprof_free_initial_handler(void *ptr);
+
+/* Fallback handlers for the main alloc/free functions. They are preset to
+ * the initializer in order to save a test in the functions's critical path.
+ */
+static void *(*memprof_malloc_handler)(size_t size)               = memprof_malloc_initial_handler;
+static void *(*memprof_calloc_handler)(size_t nmemb, size_t size) = memprof_calloc_initial_handler;
+static void *(*memprof_realloc_handler)(void *ptr, size_t size)   = memprof_realloc_initial_handler;
+static void  (*memprof_free_handler)(void *ptr)                   = memprof_free_initial_handler;
+
+/* Used to force to die if it's not possible to retrieve the allocation
+ * functions. We cannot even use stdio in this case.
+ */
+static __attribute__((noreturn)) void memprof_die(const char *msg)
+{
+	DISGUISE(write(2, msg, strlen(msg)));
+	exit(1);
+}
+
+/* Resolve original allocation functions and initialize all handlers.
+ * This must be called very early at boot, before the very first malloc()
+ * call, and is not thread-safe! It's not even possible to use stdio there.
+ * Worse, we have to account for the risk of reentrance from dlsym() when
+ * it tries to prepare its error messages. Here its ahndled by in_memprof
+ * that makes allocators return NULL. dlsym() handles it gracefully. An
+ * alternate approch consists in calling aligned_alloc() from these places
+ * but that would mean not being able to intercept it later if considered
+ * useful to do so.
+ */
+static void memprof_init()
+{
+	in_memprof++;
+	memprof_malloc_handler  = get_sym_next_addr("malloc");
+	if (!memprof_malloc_handler)
+		memprof_die("FATAL: malloc() function not found.\n");
+
+	memprof_calloc_handler  = get_sym_next_addr("calloc");
+	if (!memprof_calloc_handler)
+		memprof_die("FATAL: calloc() function not found.\n");
+
+	memprof_realloc_handler = get_sym_next_addr("realloc");
+	if (!memprof_realloc_handler)
+		memprof_die("FATAL: realloc() function not found.\n");
+
+	memprof_free_handler    = get_sym_next_addr("free");
+	if (!memprof_free_handler)
+		memprof_die("FATAL: free() function not found.\n");
+	in_memprof--;
+}
+
+/* the initial handlers will initialize all regular handlers and will call the
+ * one they correspond to. A single one of these functions will typically be
+ * called, though it's unknown which one (as any might be called before main).
+ */
+static void *memprof_malloc_initial_handler(size_t size)
+{
+	if (in_memprof) {
+		/* it's likely that dlsym() needs malloc(), let's fail */
+		return NULL;
+	}
+
+	memprof_init();
+	return memprof_malloc_handler(size);
+}
+
+static void *memprof_calloc_initial_handler(size_t nmemb, size_t size)
+{
+	if (in_memprof) {
+		/* it's likely that dlsym() needs calloc(), let's fail */
+		return NULL;
+	}
+	memprof_init();
+	return memprof_calloc_handler(nmemb, size);
+}
+
+static void *memprof_realloc_initial_handler(void *ptr, size_t size)
+{
+	if (in_memprof) {
+		/* it's likely that dlsym() needs realloc(), let's fail */
+		return NULL;
+	}
+
+	memprof_init();
+	return memprof_realloc_handler(ptr, size);
+}
+
+static void  memprof_free_initial_handler(void *ptr)
+{
+	memprof_init();
+	memprof_free_handler(ptr);
+}
+
+/* Assign a bin for the memprof_stats to the return address. May perform a few
+ * attempts before finding the right one, but always succeeds (in the worst
+ * case, returns a default bin). The caller address is atomically set except
+ * for the default one which is never set.
+ */
+static struct memprof_stats *memprof_get_bin(const void *ra)
+{
+	int retries = 16; // up to 16 consecutive entries may be tested.
+	void *old;
+	unsigned int bin;
+
+	bin = memprof_hash_ptr(ra);
+	for (; memprof_stats[bin].caller != ra; bin = (bin + 1) & (MEMPROF_HASH_BUCKETS - 1)) {
+		if (!--retries) {
+			bin = MEMPROF_HASH_BUCKETS;
+			break;
+		}
+
+		old = NULL;
+		if (!memprof_stats[bin].caller &&
+		    HA_ATOMIC_CAS(&memprof_stats[bin].caller, &old, ra))
+			break;
+	}
+	return &memprof_stats[bin];
+}
+
+/* This is the new global malloc() function. It must optimize for the normal
+ * case (i.e. profiling disabled) hence the first test to permit a direct jump.
+ * It must remain simple to guarantee the lack of reentrance. stdio is not
+ * possible there even for debugging. The reported size is the really allocated
+ * one as returned by malloc_usable_size(), because this will allow it to be
+ * compared to the one before realloc() or free(). This is a GNU and jemalloc
+ * extension but other systems may also store this size in ptr[-1].
+ */
+void *malloc(size_t size)
+{
+	struct memprof_stats *bin;
+	void *ret;
+
+	if (likely(!(profiling & HA_PROF_MEMORY)))
+		return memprof_malloc_handler(size);
+
+	ret = memprof_malloc_handler(size);
+	size = malloc_usable_size(ret);
+
+	bin = memprof_get_bin(__builtin_return_address(0));
+	_HA_ATOMIC_ADD(&bin->alloc_calls, 1);
+	_HA_ATOMIC_ADD(&bin->alloc_tot, size);
+	return ret;
+}
+
+/* This is the new global calloc() function. It must optimize for the normal
+ * case (i.e. profiling disabled) hence the first test to permit a direct jump.
+ * It must remain simple to guarantee the lack of reentrance. stdio is not
+ * possible there even for debugging. The reported size is the really allocated
+ * one as returned by malloc_usable_size(), because this will allow it to be
+ * compared to the one before realloc() or free(). This is a GNU and jemalloc
+ * extension but other systems may also store this size in ptr[-1].
+ */
+void *calloc(size_t nmemb, size_t size)
+{
+	struct memprof_stats *bin;
+	void *ret;
+
+	if (likely(!(profiling & HA_PROF_MEMORY)))
+		return memprof_calloc_handler(nmemb, size);
+
+	ret = memprof_calloc_handler(nmemb, size);
+	size = malloc_usable_size(ret);
+
+	bin = memprof_get_bin(__builtin_return_address(0));
+	_HA_ATOMIC_ADD(&bin->alloc_calls, 1);
+	_HA_ATOMIC_ADD(&bin->alloc_tot, size);
+	return ret;
+}
+
+/* This is the new global realloc() function. It must optimize for the normal
+ * case (i.e. profiling disabled) hence the first test to permit a direct jump.
+ * It must remain simple to guarantee the lack of reentrance. stdio is not
+ * possible there even for debugging. The reported size is the really allocated
+ * one as returned by malloc_usable_size(), because this will allow it to be
+ * compared to the one before realloc() or free(). This is a GNU and jemalloc
+ * extension but other systems may also store this size in ptr[-1].
+ * Depending on the old vs new size, it's considered as an allocation or a free
+ * (or neither if the size remains the same).
+ */
+void *realloc(void *ptr, size_t size)
+{
+	struct memprof_stats *bin;
+	size_t size_before;
+	void *ret;
+
+	if (likely(!(profiling & HA_PROF_MEMORY)))
+		return memprof_realloc_handler(ptr, size);
+
+	size_before = malloc_usable_size(ptr);
+	ret = memprof_realloc_handler(ptr, size);
+	size = malloc_usable_size(ptr);
+
+	bin = memprof_get_bin(__builtin_return_address(0));
+	if (size > size_before) {
+		_HA_ATOMIC_ADD(&bin->alloc_calls, 1);
+		_HA_ATOMIC_ADD(&bin->alloc_tot, size);
+	} else if (size < size_before) {
+		_HA_ATOMIC_ADD(&bin->free_calls, 1);
+		_HA_ATOMIC_ADD(&bin->free_tot, size_before);
+	}
+	return ret;
+}
+
+/* This is the new global free() function. It must optimize for the normal
+ * case (i.e. profiling disabled) hence the first test to permit a direct jump.
+ * It must remain simple to guarantee the lack of reentrance. stdio is not
+ * possible there even for debugging. The reported size is the really allocated
+ * one as returned by malloc_usable_size(), because this will allow it to be
+ * compared to the one before realloc() or free(). This is a GNU and jemalloc
+ * extension but other systems may also store this size in ptr[-1]. Since
+ * free() is often called on NULL pointers to collect garbage at the end of
+ * many functions or during config parsing, as a special case free(NULL)
+ * doesn't update any stats.
+ */
+void free(void *ptr)
+{
+	struct memprof_stats *bin;
+	size_t size_before;
+
+	if (likely(!(profiling & HA_PROF_MEMORY) || !ptr)) {
+		memprof_free_handler(ptr);
+		return;
+	}
+
+	size_before = malloc_usable_size(ptr);
+	memprof_free_handler(ptr);
+
+	bin = memprof_get_bin(__builtin_return_address(0));
+	_HA_ATOMIC_ADD(&bin->free_calls, 1);
+	_HA_ATOMIC_ADD(&bin->free_tot, size_before);
+}
+
 #endif // USE_MEMORY_PROFILING
 
 /* Updates the current thread's statistics about stolen CPU time. The unit for